Dosing and mixing arrangement for use in exhaust aftertreatment

ABSTRACT

A dosing and mixing arrangement includes a mixing tube having a constant diameter along its length. At least a first portion of the mixing tube includes a plurality of apertures. The arrangement also includes a swirl structure for causing exhaust flow to swirl outside of the first portion of the mixing tube in one direction along a flow path that extends at least 270 degrees around a central axis of the mixing tube. The arrangement is configured such that the exhaust enters an interior of the mixing tube through the apertures as the exhaust swirls along the flow path. The exhaust entering the interior of the mixing tube through the apertures has a tangential component that causes the exhaust to swirl around the central axis within the interior of the mixing tube. The arrangement also includes a doser for dispensing a reactant into the interior of the mixing tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 13/166,582,filed Jun. 22, 2011, now U.S. Pat. No. 9,670,811, which applicationclaims the benefit of provisional application Ser. No. 61/357,418entitled DOSING AND MIXING ARRANGEMENT FOR USE IN EXHAUSTAFTERTREATMENT, filed Jun. 22, 2010, which applications are incorporatedherein by reference in their entirety.

BACKGROUND

Vehicles equipped with internal combustion engines (e.g., dieselengines) typically include exhaust systems that have aftertreatmentcomponents such as selective catalytic reduction (SCR) catalyst devices,lean NOx catalyst devices, or lean NOx trap devices to reduce the amountof undesirable gases, such as nitrogen oxides (NOx) in the exhaust. Inorder for these types of aftertreatment devices to work properly, adoser injects reactants, such as urea, ammonia, or hydrocarbons, intothe exhaust gas. As the exhaust gas and reactants flow through theaftertreatment device, the exhaust gas and reactants convert theundesirable gases, such as NOx, into more acceptable gases, such asnitrogen and oxygen. However, the efficiency of the aftertreatmentsystem depends upon how evenly the reactants are mixed with the exhaustgases. Therefore, there is a need for a flow device that provides auniform mixture of exhaust gases and reactants.

SCR exhaust treatment devices focus on the reduction of nitrogen oxides.In SCR systems, a reductant (e.g., aqueous urea solution) is dosed intothe exhaust stream. The reductant reacts with nitrogen oxides whilepassing through an SCR substrate to reduce the nitrogen oxides tonitrogen and water. When aqueous urea is used as a reductant, theaqueous urea is converted to ammonia which in turn reacts with thenitrogen oxides to covert the nitrogen oxides to nitrogen and water.Dosing, mixing and evaporation of aqueous urea solution can bechallenging because the urea and by-products from the reaction of ureato ammonia can form deposits on the surfaces of the aftertreatmentdevices. Such deposits can accumulate over time and partially block orotherwise disturb effective exhaust flow through the aftertreatmentdevice.

SUMMARY

An aspect of the present disclosure relates to a dosing and mixing unitfor use in exhaust aftertreatment. The dosing and mixing unit includes amixing tube having a generally constant diameter along the length of themixing tube. The mixing tube includes a first portion having a pluralityof apertures (e.g., perforations) and a second portion having a solidwall without any apertures. The mixing tube includes a first endportioned adjacent the first portion of the mixing tube and a second endpositioned adjacent the second portion of the mixing tube. The first endof the mixing tube is closed to exhaust flow and a doser is mounted atthe first end of the mixing tube. The second end of the mixing tube isopen and functions as an outlet for the mixing tube. The dosing andmixing unit also includes a swirling structure for swirling exhaustgenerally circumferentially (i.e., tangentially) around an exterior ofthe first portion of the mixing tube. The swirling exhaust enters thefirst portion of the mixing tube through the apertures of the mixingtube. The exhaust entering the mixing tube through the apertures has atangential flow component that causes the flow to swirl within themixing tube about a central axis of the mixing tube. The swirlingexhaust then flows from the first portion of the mixing tube to thesecond portion of the mixing tube and exits the mixing tube through thesecond end of the mixing tube. The doser injects reactant into theinterior of the mixing tube and the swirling motion of the exhaustwithin the mixing tube assists in uniformly mixing the reactant into theexhaust while the exhaust is within the mixing tube.

Another aspect of the present disclosure relates to a dosing and mixingunit for use in exhaust aftertreatment. The dosing and mixing unitincludes a mixing tube having a plurality of apertures. The dosing andmixing unit also includes a swirl housing partially surrounding themixing tube. The dosing and mixing unit further includes an inlet pipeattached to a side of the swirl housing and extending out from the sideof the swirl housing in an angled tangential direction in relation to acentral axis of the mixing tube. The dosing and mixing unit alsoincludes a swirl structure for causing exhaust flow to swirl along aflow path around the central axis of the mixing tube. In addition, thedosing and mixing unit includes a doser for dispensing a reactant intothe interior of the mixing tube.

In certain embodiments, the swirling structure can include differenttypes of structures for causing the exhaust to swirl about the mixingtube. In one embodiment, the swirling structure can include an outerhousing that at least partially encloses the mixing tube and thatdirects exhaust flow in a swirling motion about the mixing tube. Inanother embodiment, the swirling structure can include a baffle thatdirects exhaust flow in a swirling motion about the mixing tube.

In certain embodiments, dosing and mixing units in accordance with theprinciples of the present disclosure can be used as part of an SCRexhaust treatment system for reducing nitrogen oxides to nitrogen andwater. In such embodiments, the dosing and mixing units can be used todose and mix reductants such as aqueous urea or ammonia at locationsupstream from SCR substrates. In other embodiments, dosing and mixingunits in accordance with the principles of the present disclosure can beused to mix other types of reactants such as hydrocarbons (e.g., fuelssuch as diesel fuel or syngas) upstream from other types of substratessuch as lean NOx catalyst devices, lean NOx traps, catalytic converterssuch as diesel oxidation catalyst (DOC) substrates and dieselparticulate filter (DPF) substrates.

A variety of additional aspects will be set forth in the descriptionthat follows. These aspects can relate to individual features and tocombinations of features. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory only and are not restrictive of the broad concepts uponwhich the embodiments disclosed herein are based.

DRAWINGS

FIG. 1 is a front view of a doser and mixing unit having features thatare examples of aspects in accordance with the principles of the presentdisclosure;

FIG. 2 is a top view of the doser and mixing unit of FIG. 1;

FIG. 3 is a cross-sectional view taken along section line 3-3 of FIG. 1;

FIG. 4 is a cross-sectional view taken along section line 4-4 of FIG. 1;

FIG. 5 is a front view of an exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 6 is a front view of another exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 7 is a front view of still another exemplary doser and mixing unitin accordance with the principles of the present disclosure;

FIG. 8 is a front view of a further exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 9 is a front view of yet an exemplary doser and mixing unit inaccordance with the principles of the present disclosure;

FIG. 10 is a top view of the doser and mixing unit of FIG. 9;

FIG. 11 is a front view of an aftertreatment device having features thatare examples of aspects in accordance with the principles of the presentdisclosure;

FIG. 12 is a top view of the aftertreatment device of FIG. 11;

FIG. 13 is a front view of a doser and mixing unit having features thatare examples of aspects in accordance with the principles of the presentdisclosure;

FIG. 14 is a schematic representation of a first exhaust treatmentsystem incorporating a doser and mixing unit in accordance with theprinciples of the present disclosure;

FIG. 15 is a schematic representation of a second exhaust treatmentsystem incorporating a doser and mixing unit in accordance with theprinciples of the present disclosure; and

FIG. 16 is a schematic representation of a third exhaust treatmentsystem incorporating a doser and mixing unit in accordance with theprinciples of the present disclosure;

FIG. 17a-17f are top views of a dosing and mixing unit showing differentmeans for creating swirl.

DETAILED DESCRIPTION

Reference will now be made in detail to the exemplary aspects of thepresent disclosure that are illustrated in the accompanying drawings.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like structure.

FIGS. 1-8 show a dosing and mixing unit 20 in accordance with theprinciples of the present disclosure. The dosing and mixing unit 20includes an inlet 22 and an outlet 24. The inlet 22 is formed by aninlet pipe 26 that extends to a swirl housing 28. The dosing and mixingunit 20 also includes a mixing tube 30 having a first end 32 positionedwithin the swirl housing 28 and a second end 34 that forms the outlet 24of the dosing and mixing unit 20. The inlet pipe 26 is attached to aside 29 of the swirl housing 28 and extends out from the side 29 of theswirl housing 28 in an angled tangential direction in relation to acentral axis 42 of the mixing tube 30. As is illustrated in FIGS. 1, 6and 7, the inlet pipe 26 can be attached to a top portion of the side 27of swirl housing 28 (see FIG. 1) or a lower portion of the side 27 ofswirl housing 28 (see FIG. 6. The inlet pipe 26 can also have differentangles in relation to the central axis 42 such that the exhaust flowenters the swirl housing 28 in a direction towards a bottom of the swirlhousing 28 (see FIGS. 1 and 6) or towards a top end 27 of swirl housing28 (see FIG. 7). In other embodiments (not shown), the inlet pipe 26 isattached to the top end 27 of swirl housing 28 in an angled tangentialdirection in relation to a central axis 42 of the mixing tube 30. Theangle between the inlet pipe 26 and the central axis 42 is in someembodiment an oblique angle.

The mixing tube 30 has a first portion 36 positioned adjacent to thefirst end 32 of the mixing tube 30 and a second portion 38 positionedadjacent to the second end 34 of the mixing tube 30. The first portion36 has a plurality of apertures 37 (e.g., perforations) and the secondportion 38 has a solid wall without any apertures. The apertures 37 canbe formed as circles, squares, slots or any other shape. The dosing andmixing unit 20 also includes a doser 40 mounted to the top end 27 of theswirl housing 28 adjacent to the first end 32 of the mixing tube 30. Thedoser 40 is adapted for dispensing reactant into an interior region ofthe mixing tube 30.

In use of the dosing and mixing unit 20, exhaust enters the dosing andmixing unit 20 through the inlet 22 and is swirled circumferentially(i.e., tangentially) through a swirl structure about the exterior of thefirst portion 36 of the mixing tube 30 by the swirl housing 28. As theexhaust flow swirls circumferentially around the first portion 36 of themixing tube 30, the exhaust gas enters the interior of the mixing tube30 through the apertures 37. The exhaust flow entering the interior ofthe mixing tube 30 through the apertures 37 has atangential/circumferential flow component that causes the exhaust toswirl within the interior of the mixing tube 30. The doser 40 dispensesreactant into the swirling exhaust within the interior of the mixingtube where the swirling action of the exhaust assists in uniformlymixing the reactant within the exhaust. Swirling flow of the exhaustcontinues from the first portion 36 of the mixing tube 30 to the secondportion 38 of the mixing tube 30 whereby mixing is enhanced as theexhaust moves through the length of the mixing tube 30. After theswirling exhaust has traveled through the mixing tube in a directionextending from the first end 32 to the second end 34 of the mixing tube30, the exhaust exits the dosing and mixing unit 20 through the outlet24. As is seen in FIG. 2, the swirl structure has in some embodiments across-section that gradually decreases along the exhaust flow path.

The mixing tube 30 of the dosing and mixing unit 20 defines the centralaxis 42 and has a length that extends along the central axis 42 from thefirst end 32 to the second end 34 of the mixing tube 30. The mixing tube30 is cylindrical in shape and has in some embodiments (shown in FIGS.1-7) a constant diameter along the entire length of the mixing tube 30.Thus, the first and second portions 36, 38 of the mixing tube 30 haveconstant diameters along their respective lengths. Also, the first andsecond portions 36, 38 of the mixing tube 30 are shown having equaldiameters. In some embodiments (shown in FIG. 8), the first end 32 ofthe mixing tube 30 has a larger diameter than the second end 34. In someembodiments, the first portion 36 of the mixing tube 30 has a diameterthat gradually decreases along its length towards the second portion 38.The first end 32 of the mixing tube 30 is blocked by the top end 27 ofswirl housing 28 so that exhaust flow can not pass through the first end32 of the mixing tube 30. In some embodiments, as is seen in FIGS. 5 and8, the first end 32 of the mixing tube 30 is arranged at a distance fromthe top end 27 of the swirl housing 28, forming a gap 52. The doser 40is positioned at the first end 32 of the mixing tube 30 and is alignedalong the central axis 42. As shown at FIGS. 3 and 4, the swirlingmotion of the exhaust can increase in intensity as the swirling exhaustmoves axially through the first portion 36 of the mixing tube in adirection toward the second portion 38 of the mixing tube 38. Thus, bythe time the exhaust enters the second portion 38 of the mixing tube 30,the exhaust is swirling at an increased rate.

In certain embodiments, the doser 40 can include an injector thatinjects reactant in a spray cone aligned along the central axis 42 ofthe mixing tube 30. The swirling action of the exhaust and theconverging flow passing through the apertures 37 (see FIG. 3) assists innarrowing the spray cone angle thereby inhibiting wetting of theinterior of the mixing tube 30 and minimizing deposit formation withinthe mixing tube and downstream from the mixing tube. The swirling actionis particularly suited for breaking-up, mixing and evaporating aqueousurea in a relatively short time frame/distance.

The swirl housing 28 at least partially encloses the first portion 36 ofthe mixing tube 30 and has an arrangement that directs exhaust flowtangentially relative to the outer surface of the mixing tube 30 suchthat the exhaust swirls circumferentially around the exterior of themixing tube 30. In one embodiment, the exhaust flows in a singledirection (e.g., clockwise relative to the central longitudinal axis asshown at FIG. 2) around at least 75 percent of the outer diameter of themixing tube 30. In other words, the exhaust flow direction turns atleast 270 degrees around the outer diameter of the mixing tube 30. Asthe exhaust flows around the mixing tube 30, portions of the exhaustprogressively enter the interior of the first portion 36 of the mixingtube 30 through the apertures 37. The swirl housing 28 has a curved/bentsurface 44 that curves along and opposes the outer surface of the firstportion 36 of the mixing tube 30. The surface 44 is arranged totransition progressively closer to the outer surface of the firstportion 36 of the mixing tube 30 as the surface extends in thecircumferential direction of exhaust flow. In some embodiments (notshown), the mixing tube 30 is arranged such in the swirl housing 28 thatthe central axis 42 of the mixing tube 30 is not in parallel with alongitudinal axis of the swirl housing 28, i.e. the second portion 28 ofthe mixing tube 30 extends from the swirl housing 28 in an angleddirection.

FIGS. 9 and 10 show a dosing and mixing unit 20 that is configured inthe same manner and includes the same features as described inconjunction with FIGS. 1-8. The unit 20 further comprises indents 62 orsome other kind of profile for causing the exhaust to swirl within theinterior of the mixing tube 30. In some embodiments (not shown), theswirl housing 28 includes indents or other kinds of profiles on theinside of the top end 27 for causing the swirl. In other embodiments,the unit 20 includes a screw or helical shaped device arranged aroundthe mixing tube 30 for causing the exhaust to swirl.

FIGS. 11 and 12 show an aftertreatment device 120 in accordance with theprinciples of the present disclosure. The aftertreatment device 120includes an inlet 122 and an outlet 124. The inlet 122 is formed by aninlet pipe 126 that extends to a substrate housing 128. A substrate 129(e.g., a DPF substrate or DOC substrate) is positioned within thesubstrate housing 128 adjacent to the inlet pipe 126. The aftertreatmentdevice 120 also includes a mixing tube 130 having the same configurationas the mixing tube 30. The mixing tube 130 has a first end 132positioned within the substrate housing 128 and a second end 134 thatforms the outlet 124 of the aftertreatment device 120. The mixing tube130 has a first portion 136 positioned adjacent to the first end 132 ofthe mixing tube 130 and a second portion 138 positioned adjacent to thesecond end 134 of the mixing tube 130. The first portion 136 has aplurality of apertures 137 (e.g., perforations) and the second portion138 has a solid wall without any apertures. The apertures 137 can beformed as circles, squares, slots or any other shape. The aftertreatmentdevice 120 also includes a doser 140 mounted to the housing 128 adjacentto the first end 132 of the mixing tube 130. The doser 140 is adaptedfor dispensing reactant into an interior region of the mixing tube 130.A deflector baffle 150 is positioned between the substrate 129 and thefirst portion 136 of the mixing tube 130. The deflector baffle 150 isconfigured to cause the exhaust to flow circumferentially in onedirection around at least 270 degrees of the exterior of the outerdiameter of the first portion 136 of the mixing tube 30. The baffle 150directs the flow in a tangential direction relative to the outerdiameter of the mixing tube 30. In certain embodiments, the mixing tube130 can be bent so that an out put end of the tube angles away from theinlet 122. In other embodiments, the tube 130 can be straight and theentire tube 130 can be angled at angle θ relative to a central axis ofthe housing 128. In certain embodiments, the angle θ is in the range of60-90 degrees. In other embodiments, the angle θ is less than 90degrees, or less than 80 degrees, or in the range of 60-80 degrees. Inother embodiments, the angle θ is 90 degrees. The angle θ is measuredbetween the outer end of the tube 130 and the main body of the housing128.

In another embodiment, the tube 130 can be offset from the center of thehousing 128 so as to be closer to a first side 131 (e.g., a top side) ofthe housing as compared to a second side 133 (e.g., a bottom side) ofthe housing 128.

In use of the aftertreatment device 120, exhaust enters the device 120through the inlet 122 and passes through the substrate 129 where theexhaust is initially treated (e.g., contaminants removed by filtrationor chemically through a catalyzed reaction at the substrate). After theexhaust passes through the substrate 129, the baffle 150 causes theexhaust to swirl circumferentially (i.e., tangentially) through a swirlstructure about the exterior of the first portion 136 of the mixing tube130. As the exhaust flow swirls circumferentially around the firstportion 136 of the mixing tube 130, the exhaust gas enters the interiorof the mixing tube 130 through the apertures 137. The exhaust flowentering the interior of the mixing tube 130 through the apertures 137has a tangential/circumferential flow component that causes the exhaustto swirl within the interior of the mixing tube 130. The doser 140dispenses reactant into the swirling exhaust within the interior of themixing tube where the swirling action of the exhaust assists inuniformly mixing the reactant within the exhaust. Swirling flow of theexhaust continues from the first portion 136 of the mixing tube 130 tothe second portion 138 of the mixing tube 130 whereby mixing is enhancedas the exhaust moves through the length of the mixing tube 130. Afterthe swirling exhaust has traveled through the mixing tube in a directionextending from the first end 132 to the second end 134 of the mixingtube 130, the exhaust exits the device 120 through the outlet 124. As isseen in FIG. 12, the swirl structure has a cross-section that graduallydecreases along the exhaust flow path.

FIG. 13 shows a doser and mixing unit 220 in accordance with theprinciples of the present disclosure. The unit 220 includes an inlet 222and an outlet 224. The inlet 222 is formed by an inlet pipe 226 thatextends to a swirl housing 128. The unit 220 also includes a mixing tube230 having the same configuration as the mixing tube 30 shown anddescribed in conjunction with FIGS. 1-10. As can be seen in FIG. 13, theinlet pipe 226 is arranged with a radial offset from a central axis ofthe mixing tube 230 such that the incoming exhaust through the inlet 222has a flow direction that is generally in parallel of the direction ofthe outgoing exhaust through outlet 224. The mixing tube 230 has a firstend 232 positioned within the swirl housing 228 and a second end 234that forms the outlet 224 of the unit 220. The mixing tube 230 has afirst portion 236 positioned adjacent to the first end 232 of the mixingtube 230 and a second portion 238 positioned adjacent to the second end234 of the mixing tube 230. The first portion 236 has a plurality ofapertures 237 (e.g., perforations) and the second portion 238 has asolid wall without any apertures. The apertures 237 can be formed ascircles, squares, slots or any other shape. The unit 220 also includes adoser 240 mounted to the housing 228 adjacent to the first end 232 ofthe mixing tube 230. The doser 240 is adapted for dispensing reactantinto an interior region of the mixing tube 230. A deflector baffle 250is positioned within the swirl housing 228 between the inlet pipe 226and the first portion 236 of the mixing tube 230. The deflector baffle250 is configured to cause the exhaust to flow circumferentially in onedirection around at least 270 degrees of the exterior of the outerdiameter of the first portion 236 of the mixing tube 230. The baffle 250directs the flow in a tangential direction relative to the outerdiameter of the mixing tube 230.

As the exhaust flow swirls circumferentially around the first portion236 of the mixing tube 230, the exhaust gas enters the interior of themixing tube 230 through the apertures 237. The exhaust flow entering theinterior of the mixing tube 230 through the apertures 237 has atangential/circumferential flow component that causes the exhaust toswirl within the interior of the mixing tube 230. The doser 240dispenses reactant into the swirling exhaust within the interior of themixing tube where the swirling action of the exhaust assists inuniformly mixing the reactant within the exhaust. Swirling flow of theexhaust continues from the first portion 236 of the mixing tube 230 tothe second portion 238 of the mixing tube 230 whereby mixing is enhancedas the exhaust moves through the length of the mixing tube 230. Afterthe swirling exhaust has traveled through the mixing tube 230 in adirection extending from the first end 232 to the second end 234 of themixing tube 230, the exhaust exits the unit 220 through the outlet 224.

FIG. 14 shows a system 300 including the dosing and mixing unit 20. Thesystem includes an internal combustion engine 302. A pipe 304 carriesexhaust from the engine 302 to the dosing and mixing unit 20 wherereactant (e.g., aqueous urea) is injected into the exhaust stream andmixed with the exhaust stream. A pipe 306 carries the exhaust streamcontaining the reactant to an SCR device 308 where nitrogen oxides arereduced to nitrogen and water. FIG. 15 shows a system 400 that is thesame as the system 300 except a separate aftertreatment substrate (e.g.,a DPF or DOC) is positioned between the engine 300 and the dosing andmixing unit 20. FIG. 16 shows a system 500 that is the same as thesystem 300 except the aftertreatment device 120 has been substituted forthe dosing and mixing unit 20.

A selective catalytic reduction (SCR) catalyst device is typically usedin an exhaust system to remove undesirable gases such as nitrogen oxides(NOx) from the vehicle's emissions. SCR's are capable of converting NOxto nitrogen and oxygen in an oxygen rich environment with the assistanceof reactants such as urea or ammonia, which are injected into theexhaust stream upstream of the SCR through the doser 40. In alternativeembodiments, other aftertreatment devices such as lean NOx catalystdevices or lean NOx traps could be used in place of the SCR catalystdevice, and other reactants (e.g., hydrocarbons) can be dispensed by thedoser.

A lean NOx catalyst device is also capable of converting NOx to nitrogenand oxygen. In contrast to SCR's, lean NOx catalysts use hydrocarbons asreducing agents/reactants for conversion of NOx to nitrogen and oxygen.The hydrocarbon is injected into the exhaust stream upstream of the leanNOx catalyst. At the lean NOx catalyst, the NOx reacts with the injectedhydrocarbons with the assistance of a catalyst to reduce the NOx tonitrogen and oxygen. While the exhaust treatment systems 400 and 500will be described as including an SCR, it will be understood that thescope of the present disclosure is not limited to an SCR as there arevarious catalyst devices that can be used in accordance with theprinciples of the present disclosure.

The lean NOx traps use a material such as barium oxide to absorb NOxduring lean burn operating conditions. During fuel rich operations, theNOx is desorbed and converted to nitrogen and oxygen by reaction withhydrocarbons in the presence of catalysts (precious metals) within thetraps.

FIGS. 17a-17f are top views of a dosing and mixing unit 20 as describedand shown in conjunction with FIGS. 1-10 and show different means forcreating exhaust flow swirl. FIG. 17a illustrates a swirl structure thathas the same cross-section around the outer diameter of the mixing tube30. In the embodiment shown in FIG. 17b , the swirl housing 28 includesa stop wall 63 that forces the exhaust flow to enter the mixing tube 30.In the embodiment shown in FIG. 17c , the dosing and mixing unit 20includes one or more flow guide devices 64 arranged between an outerwall of the mixing tube 30 and an inner wall of the swirl housing 28.The flow guide devices 64 may extend from a bottom of the swirl housing28 or from a top of the swirl housing 28. The flow guide device(s) 64may also be arranged on the inner wall of the swirl housing 28 (as shownin FIG. 17d ) or on the outer wall of the mixing tube 30 (not shown).Further, according to some embodiments, the mixing tube 30 may beprovided with fins 65 inwardly extending from an inner wall of themixing tube 30 (see FIG. 17e ). FIG. 17f illustrates that swirlstructure transits from a circular cross-section into an oval orelliptical cross-section along the flow path.

Various modifications and alterations of this disclosure will becomeapparent to those skilled in the art without departing from the scopeand spirit of this disclosure, and it should be understood that thescope of this disclosure is not to be unduly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A unit for an exhaust system, the unitcomprising: a mixing tube including a circumferential wall extendingbetween a first end and a second end, the circumferential wall defininga plurality of apertures spaced about a circumference of the mixingtube; an inlet pipe and an outlet pipe, the outlet pipe being co-axiallyaligned with the mixing tube; an exhaust treatment substrate positionedat a location between the inlet pipe and the mixing tube, the exhausttreatment substrate defining a central axis that intersects the mixingtube; at least one flow deflection surface arranged to cause exhaustflow entering the mixing tube through the apertures to swirl within aninterior of the mixing tube, the at least one flow deflection surfaceincluding a baffle positioned between the inlet pipe and the mixing tubefor deflecting exhaust about the mixing tube in one rotational directionalong a flow path that extends at least 270 degrees about the mixingtube, the baffle extending across at least a majority of a diameter ofthe mixing tube; and a doser mounting location defined at the first endof the mixing tube.
 2. The unit of claim 1, wherein the exhausttreatment substrate is a diesel oxidation catalyst or a dieselparticulate filter.
 3. The unit of claim 1, wherein the mixing tube istransversely aligned relative to the central axis of the exhausttreatment substrate.
 4. The unit of claim 1, wherein the at least oneflow deflection surface includes a flow deflection surface defined bythe baffle.
 5. The unit of claim 1, wherein the mixing tube is integralwith the outlet pipe.
 6. The unit of claim 1, wherein the mixing tubedefines a tube axis, and wherein the at least one flow deflectionsurface includes flow deflection surfaces arranged and configured tocause exhaust to flow around the tube axis about an exterior of themixing tube.
 7. The unit of claim 1, further comprising a doser mountedat the doser mounting location, the doser being configured for directinga reactant into the interior of the mixing tube.
 8. The unit of claim 7,further comprising a source of aqueous urea that supplies aqueous ureato the doser.
 9. The unit of claim 1, wherein the mixing tube defines atube axis, and wherein the at least one flow deflection surface includesa plurality of flow guide surfaces positioned around the tube axis. 10.The unit of claim 9, wherein the flow guide surfaces are integral withthe mixing tube and positioned at apertures of the mixing tube.
 11. Theunit of claim 1, wherein the at least one deflection surface includes aflow deflection surface defined by the baffle positioned between theexhaust treatment substrate and the mixing tube, the flow deflectionsurface of the baffle being intersected by the central axis of theexhaust treatment substrate.
 12. The unit of claim 11, wherein thebaffle is configured for directing exhaust flow toward one side of themixing tube.
 13. The unit of claim 12, wherein the mixing tube defines atube axis, and wherein the baffle and an outer housing of the unit arearranged and configured to cooperate such that the exhaust flows in onedirection around the tube axis about an exterior of the mixing tube. 14.A unit for treating, dosing and mixing exhaust, the unit comprising: amixing tube having a central axis extending along a length of the mixingtube, the mixing tube including a plurality of apertures spaced about acircumference of the mixing tube; a housing in which the mixing tube isat least partially positioned, the housing having a longitudinal axisthat is transversely aligned relative to the mixing tube, the unitincluding an inlet pipe and an outlet pipe that project outwardly fromthe housing, the outlet pipe being co-axially aligned with the mixingtube; an exhaust treatment substrate positioned within the housing at alocation between the inlet pipe and the mixing tube, the exhausttreatment substrate being aligned along the longitudinal axis of thehousing; and a swirl structure for causing exhaust flow exiting theexhaust treatment substrate flow to swirl within the housing around anoutside of the mixing tube along a flow path that extends around thecentral axis of the mixing tube, wherein the exhaust enters an interiorof the mixing tube through the apertures as the exhaust swirls along theflow path, and wherein the exhaust entering the interior of the mixingtube through the apertures swirls around the central axis within theinterior of the mixing tube, the swirl structure including a main baffleplate spaced from the mixing tube at a location between the exhausttreatment substrate and the mixing tube.
 15. The unit of claim 14,wherein the exhaust treatment substrate is selected from the groupconsisting of a catalytic converter and a diesel particulate filter. 16.The unit of claim 14, wherein the flow path extends at least 270 degreesin one rotational direction about the central axis of the mixing tube.17. The unit of claim 14, wherein the longitudinal axis of the housingintersects the mixing tube and the longitudinal axis is perpendicularrelative to the central axis of the mixing tube.
 18. The unit of claim14, wherein the outlet pipe is integral with the mixing tube.
 19. Theunit of claim 14, wherein the housing is configured such that all of theexhaust is required to flow through the mixing tube before beingdischarged from the unit.
 20. The unit of claim 14, wherein the inletand outlet pipes are generally perpendicular relative to one another.21. The unit of claim 14, wherein a doser is mounted to the housingadjacent one end of the mixing tube.
 22. The unit of claim 14, whereinthe main baffle plate extends from the housing and forces flow to oneside of the mixing tube.
 23. The unit of claim 14, wherein a section ofthe mixing tube that defines the apertures overlaps an end face of theexhaust treatment substrate.
 24. The unit of claim 14, furthercomprising: a source of aqueous urea; and a doser for dispensing aqueousurea from the source of aqueous urea, the aqueous urea dispensed fromthe doser being mixed with the swirling exhaust within the interior ofthe mixing tube.
 25. A unit for treating, dosing and mixing exhaust, theunit comprising: a mixing tube having a central axis extending along alength of the mixing tube, the mixing tube including a plurality ofapertures spaced about a circumference of the mixing tube; a housing inwhich the mixing tube is at least partially positioned, the housinghaving a first end and an opposite second end, the unit including aninlet adjacent the first end of the housing and an outlet adjacent thesecond end of the housing, the inlet and the outlet being angledrelative to one another so that axes defined by the inlet and the outletare not parallel, and the outlet being co-axially aligned with themixing tube; a swirl structure for causing exhaust flow to swirl withinthe housing outside of the mixing tube in one rotational direction alonga flow path that extends at least 270 degrees around the central axis ofthe mixing tube, wherein the exhaust enters an interior of the mixingtube through the apertures as the exhaust swirls along the flow path,and wherein the exhaust entering the interior of the mixing tube throughthe apertures swirls around the central axis within the interior of themixing tube, the swirl structure including a main baffle positionedbetween the inlet and the mixing tube for deflecting exhaust toward oneside of the mixing tube, the main baffle extending from the housingacross at least a majority of a diameter of the mixing tube; an exhausttreatment substrate positioned within the housing at a location betweenthe inlet and the main baffle, the exhaust treatment substrate beingaligned along a longitudinal axis of the housing that extends betweenthe first and second ends of the housing and is oriented to intersectthe mixing tube, and the mixing tube being transversely orientedrelative to the longitudinal axis of the housing.
 26. The unit of claim25, wherein the housing is configured such that all of the exhaust isrequired to flow through the mixing tube before being discharged fromthe unit.
 27. The unit of claim 25, wherein the apertures are circular.28. The unit of claim 25, wherein the apertures are arranged in rowsthat extend along a length of the mixing tube.
 29. The unit of claim 25,wherein the main baffle extends from the housing across the entirediameter of the mixing tube.
 30. The unit of claim 25, wherein theapertures are each substantially smaller than the main baffle and arearranged in rows having row lengths that extend along the central axisof the mixing tube, wherein the rows have row lengths, and wherein themain baffle extends along at least a majority of the distance defined byeach row length.
 31. The unit of claim 25, further comprising: a sourceof aqueous urea; and a doser for dispensing aqueous urea from the sourceof aqueous urea into the interior of the mixing tube for mixing with theswirling exhaust within the interior of the mixing tube.